# Coroutine support (C++20)

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The coroutine support library defines several types that provide compile and run-time support for coroutines.

### Coroutine traits

Defined in header `<coroutine>`
coroutine_traits (C++20) | trait type for discovering coroutine promise types (class template)

### Coroutine handle

Defined in header `<coroutine>`
coroutine_handle (C++20) | used to refer to a suspended or executing coroutine (class template)

### No-op coroutines

Defined in header `<coroutine>`
noop_coroutine (C++20) | creates a coroutine handle that has no observable effects when resumed or destroyed (function)
noop_coroutine_promise (C++20) | used for coroutines with no observable effects (class)
noop_coroutine_handle (C++20) | std::coroutine_handle<std::noop_coroutine_promise>, intended to refer to a no-op coroutine (typedef)

### Trivial awaitables

Defined in header `<coroutine>`
suspend_never (C++20) | indicates that an await-expression should never suspend (class)
suspend_always (C++20) | indicates that an await-expression should always suspend (class)

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_impl_coroutine` | `201902L` | (C++20) | Coroutines (compiler support)
`__cpp_lib_coroutine` | `201902L` | (C++20) | Coroutines (library support)
`__cpp_lib_generator` | `202207L` | (C++23) | std::generator: synchronous coroutine generator for ranges

### See also

generator (C++23) | A `view` that represents synchronous coroutine generator (class template)

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